The invention relates to an electrolytic capacitor having a substantially non-aqueous fill electrolyte solution of a low resistivity which is suitable for use up to high operating voltages.
A fill electrolyte solution for electrolytic capacitors must satisfy a number of important requirements.
The solution must be capable of maintaining the dielectric oxide film provided on the anode by forming at the applied voltage. In particular at a high voltage, for example 385 V, no dielectric breakdowns may occur: the spark voltage or breakdown voltage of the solution must be sufficiently high.
The restivity of the electrolyte solution must be low because it contributes to the equivalent series resistance (esr, measured at higher frequencies of 10-100 kHz.
It has been found in practice so far that the combined properties of a high breakdown voltage and a low resistivity are difficult to realize in one electrolyte solution. For these reasons it was usual to use different solutions for the various voltage ranges. For example, known solutions for use in electrolytic capacitors of 385-400 V have a resistivity of 1000-2000 .OMEGA. cm at 20.degree. or even higher.
Recent new applications of electrolytic capacitors require a reduction of the dielectric losses. In particular the impedance Z at 10-100 kHz must be low, inter alia to ensure a sufficient ripple current load.
From German Offenlegungsschrift No. 15 89 671, for example, a capacitor is known which comprises an electrolyte solution having one or more aprotic dipolar solvents in which an amine and one or more acids are dissolved. The solutions belong to those which do not have the desired combination of properties.